Found some more differences. Botswana and Togo can be explained by the Botswana-Chad and the Togo-Malawi matches. All others have only 1 point difference. Canada is the only one with 2 points difference.

Average all the results from Malawi's matches in the last 12 months. They have played 13 matches in that period, earning a total of about 3518.6 points (if I did the math right). Dividing that by 13 gives an average of 270.7. That is the first part of Malawi's overall total.

For the 2nd, 3rd, and 4th parts of the total, you would do the same thing for the matches from 13-24, 25-36, and 37-48 months ago to get an average for each of those periods. But then you need to multiply each of those averages by 0.5, 0.3, and 0.2, respectively, before adding them to the overall total.